A film to be used as packaging materials for food, non-food products, medicines, and the like and as members of electronic apparatuses is required to have gas barrier properties which prevent oxygen, water vapor, and some other gases which deteriorate the contents from passing through the film, in order to suppress deterioration of the contents and maintain the functions and properties of the contents. As films having ordinary gas barrier levels, a vinylidene chloride resin film having relatively good gas barrier properties as a polymer and a laminated film coated with this vinylidene chloride resin film are often used. However, these films are unsatisfactory when high gas barrier levels are required. Therefore, it is necessary to use a laminated film containing a metal foil made of a metal such as aluminum.
This laminated film containing a metal foil or the like has high-level gas barrier properties regardless of temperature and humidity. However, this laminated film has many problems, e.g., the film must be discarded as an incombustible material after used, the weight per unit area of the film is large, and the contents cannot be inspected by a metal detector.
As packaging materials which have solved these problems, U.S. Pat. No. 3,442,686, Jpn. Pat. Appln. KOKOKU Publication No. 63-28017, and the like disclose deposited films which metal oxides, e.g., inorganic oxides such as silicon oxide, aluminum oxide, and magnesium oxide are deposited on plastic films by using depositing method such as vacuum deposition method and sputtering method. These deposited films are regarded as suitable for packaging materials which have transparency unobtainable by metal foils, which have gas barrier properties against gases such as oxygen and water vapor, and which are light in weight and readily disposable.
Such deposited films are not singly used as packaging materials in most cases. For example, a deposited film is processed into a packaging material through various steps of, e.g., printing characters and patterns on the surface of the deposited film, bonding the deposited film on another film, and processing the deposited film into a packaging material such as a vessel.
The abovementioned deposited films were bonded on a sealant film and the barrier properties such as the oxygen permeability and the water vapor permeability were measured. As a consequence, the gas barrier properties were equal or superior to those of polymeric gas-barrier films, but did not reach the gas barrier properties of metal foils.
As described above, the conventional deposited films are light in weight and readily disposable, realize high transparency, and allow inspection of contents by a metal detector. However, no such high-level gas barrier properties as those of metal foils cannot be obtained.